Optical fiber is increasingly used in a variety of applications ranging from long distance voice and data transmission to interconnection of electronic devices, subassemblies, or assemblies. In many, perhaps all, applications of optical fiber, it is necessary to couple a source of electromagnetic radiation of appropriate wavelength such as a light-emitting diode or a semiconductor laser to the fiber, and/or to couple a detector of electromagnetic radiation (e.g., a PIN diode) to the fiber.
Although there exist many applications (e.g., in intercontinental or inter-city optical fiber communications systems) that demand very high coupling efficiency, there are also many significant applications (e.g., in the local loop portions of fiber communication systems, in local area networks, or optical interconnects of components of electronic systems such as 5ESS.RTM. electronic switches) that do not require such high coupling efficiency. In the latter case coupling losses of 1 db and even high frequently will be acceptable. Relaxation of coupling efficiency requirements typically translates into a simpler design and thus into a lower cost coupling means.
The desirability of providing moderately efficient, inexpensive and compact means for optically coupling an opto-electronic device to the end of a fiber has become recognized. Desirably, such means are compatible with IC (integrated circuit) mounting technology, since such compatibility typically simplifies assembly and thus results in significant cost reduction. For an example of an advanced mounting technique see, for instance, U.S. Pat. No. 4,675,717, incorporated herein by reference.
A fiber-to-device coupling assembly that is compatible with IC technology is disclosed in U.S. patent Ser. No. 4,779,946, filed Feb. 14, 1986 for R. J. Pimpinella and J. M. Segelken, incorporated herein by reference. This prior art coupling assembly utilizes a Si chip comprising a through-aperture to maintain the end of an optical fiber in coupling relationship with an opto-electronic component mounted on the chip. The chip exemplarily is produced by a process that comprises selective etching of one face of a Si wafer to form sloped-wall through-apertures, formation of metallization patterns on the other face of the wafer in precise alignment with respect to these apertures, and dicing of the wafer. The end of an optical fiber is inserted into the aperture and maintained therein by appropriate means, and an appropriate opto-electronic device (transducer) is aligned with the metallization pattern and conductively attached thereto. Alignment between the core of the optical fiber and the active area of the transducer results from the precise placement of the metallization pattern and the alignment of the transducer with the pattern. The thus formed assembly can then be mounted on an appropriate substrate (e.g., a Si wafer with appropriate metallization thereon) substantially in the same manner as ordinary IC chips, e.g., by means of a face-down solder ball technique.
Although providing a significant advance over other prior art coupling assemblies, the above described assembly has some shortcomings. In particular, the assembly requires use of conductive "contact blocks" to make possible mounting of the assembly on a laterally extending substrate, e.g., a silicon wafer as used in the above referred to advanced interconnection method. Such contact blocks are relatively large and therefore limit the maximum frequency of operation of the assembly, due to the relatively high capacitance associated with the contact blocks. Furthermore, in order to attain acceptable optical coupling between the fiber and a transducer the metallization patterns have to be in accurate alignment with the fiber-receiving aperture (which frequently is difficult to achieve), and the transducer has to be affixed to the face of the silicon block in precise registry with the metallization pattern. Typically, no opportunity exists to compensate for such unavoidable imperfections as variations in the placement of the active area of the opto-electronic device relative to the metallization pattern.
In view of the above discussion, it will be apparent that compact, relatively low cost means for coupling an optical fiber to an opto-electronic device that are compatible with current and many anticipated IC mounting techniques and that are compatible with the relatively high signal transmission rates that are possible in optical fiber communications would be highly desirable. We are disclosing herein such coupling means.